1. Field of the Invention
The present invention relates to a constellation rotation relay system and a constellation rotation relay method thereof. More particularly, the present invention relates to a constellation rotation relay system and a constellation rotation relay method which can acquire full diversity gain by performing a constellation rotation process for a channel matrix in a relay network, when configuring a virtual multiple input multiple output (MIMO) channel.
2. Description of Related Art
A relay network is used for maintaining communication in a shadow region and extending a coverage area of a cell. Communication performance between a base station and a mobile station may be improved by employing a relay.
FIG. 1, parts i), ii), and iii) are diagrams illustrating an example of a protocol applied to a relay network in related art.
As illustrated in FIG. 1 parts i), ii), and iii), there is a MIMO, a single input multiple output (SIMO), and a multiple input single output (MISO) protocols provided in a conventional relay network.
In FIG. 1 parts i), ii), and iii), S, R, and D respectively indicate a source, a relay and a destination, and a dotted line indicates a transmission comprising different symbols.
FIG. 1 part i) relates to a MIMO protocol. A source in a first time slot transmits a first symbol to a relay and a destination. Also, the source in a second time slot transmits a second symbol to the destination, and the relay transmits the symbol, received in the first time slot, to the destination by applying an amplify-and-forward (AF) or a decode-and-forward (DF) function. In the AF function the received symbol is power amplified in the relay and then retransmitted. In the DF function, the received symbol is decoded and then re-encoded. The re-encoded symbol is then power amplified and transmitted.
FIG. 1 part ii) relates to a SIMO protocol. Operation in a first time slot is identical to the MIMO protocol, and a relay operates identical to the MIMO protocol, however the source in a second time slot does not operate.
FIG. 1 part iii) relates to a MISO protocol. A source in a first time slot transmits a first symbol to a relay, the source in a second time slot retransmits the first symbol, and the relay transmits the symbol, received in the first time slot, to a destination by applying the AF function or the DF function.
As shown in Equation 1, the MIMO protocol has an advantage of having a twice the transmission rate of the SIMO protocol and the MISO protocol.yR,1=hSRx1+nR,1 yD,1=hSDx1+nD,1 yD,2=hRD{circumflex over (x)}1+hSDx2+nD,2 
Equation 1 indicates input/output equations in a relay and a destination with respect to the MIMO protocol using the DF system. The S, R and D in Equation 1 respectively indicates a source, a relay and a destination, and the subscripts “1” and “2” indicate a time slot. Also, y indicates a receiving signal, x indicates an input signal, h indicates a channel value, n indicates white noise, and {circumflex over (x)}1 indicates a decoded symbol.
                              [                                                                      y                                      D                    ,                    1                                                                                                                        y                                      D                    ,                    2                                                                                ]                =                                                                              [                                                                                                              h                          SD                                                                                            0                                                                                                                                      h                          RD                                                                                                                      h                          SD                                                                                                      ]                                ⁡                                  [                                                                                                              x                          1                                                                                                                                                              x                          2                                                                                                      ]                                            +                              [                                                                                                    n                                                  D                          ,                          1                                                                                                                                                                        n                                                  D                          ,                          2                                                                                                                    ]                                      ⁢                                                  →            Y                    =                      Hx            +            N                                              [                  Equation          ⁢                                          ⁢          2                ]            
When Equation 1 is represented into a matrix, Equation 1 is represented as Equation 2. In Equation 2, when the relay decodes the symbol to x1 via a perfect decoding process, ‘{circumflex over (x)}1=x1’ may be tenable. Accordingly, the MIMO protocol may configure a virtual MIMO channel environment as shown in Equation 2.
In Equation 2, conversely, a conventional MIMO system, one of the channel values of the channel matrix H becomes ‘0’, subsequently full diversity gain may not be acquired. Only a first order diversity in the virtual MIMO channel environment by the MIMO protocol may be gained due to the ‘0’ channel value even if a signal-to-noise ratio with respect to a link between the source and the relay is greater.
Accordingly, a new relay system which can constellation rotate a channel value by multiplying the constellation with a predetermined matrix, and thereby may acquire full diversity gain when configuring a virtual MIMO equivalence channel, is required.